Ti alloys are used as compressor blades and disks in jet engines due to their high specific strength and good oxidation resistance at operation temperature. However, Ti alloys cannot be used above 600 °C because creep properties and oxidation resistance deteriorate. To overcome the above problems, the effect of alloying element on oxidation resistance was investigated and it was found that Sn deteriorated oxidation resistance and Nb improved oxidation resistance. Then, we have attempted to design new Ti alloys without Sn, but including Nb because Nb improved oxidation resistance. To expect solid-solution hardening, Zr was also added to the alloys. In this study, the creep behavior of Ti-10Al-2Nb-2Zr and Ti-10Al-2Nb-2Zr-0.5Si alloys was investigated. The creep test was performed at temperature range between 550 and 650 °C and stress range between 137 and 240 MPa. The stress exponent and the activation energy for creep were analyzed using an Arrhenius equation. The stress exponent was 5.9 and 3.4, and the activation energy was 290 and 272 kJ/mol for Ti-10Al-2Nb-2Zr and Ti-10Al-2Nb-2Zr-0.5Si, respectively. This indicates the creep deformation mechanism is dislocation (high-temperature power law) creep governed by lattice diffusion.

Understanding of the thermomechanical processing that affects microstructures is important to develop new alloys, because the mechanical properties of Ti alloys depend on the microstructures. In our previous study, we found Sn deteriorated the oxidation resistance, while Nb improved the oxidation resistance. Then, we have focused on Ti-Al-Nb-Zr alloys which Nb was added instead of Sn. Zr was added for solid solution strengthening. In this study, the formation of microstructures by thermomechanical processing and the effect of microstructure on the mechanical properties were investigated using the Ti-13Al-2Nb-2Zr (at%) alloy. The samples heat-treated in the β+α phase followed by furnace cooling after processed in the β+α phase formed the equiaxed or the ellipsoid α phase surrounded by the β phase. On the other hand, the sample heat-treated in the β+α phase followed by furnace cooling after processed in the β phase formed the lamellar microstructure. The compression strengths of the equiaxed α structure processed at two temperatures in the β+α phase were almost the same. While creep life of the bi-modal structure was drastically changed by processing temperature.

High-temperature shape memory alloys (HTSMAs) are expected to be utilized for actuators in high temperature environments such as thermal power plants and jet engines. NIMS has designed TiPd shape memory alloys because high martensitic phase transformation temperature of TiPd around 570 ° C is expected to be high-temperature shape memory alloys. However, the strength of the austenite phase of TiPd is low and the perfect recovery was not obtained. Then, strengthening of TiPd by addition of alloying elements has been attempted, but the complete recovery was not obtained. Therefore, high entropy alloys (HEA, multi-component equiatomic or near equiatomic alloys) were attempted for HTSMA. The severe lattice distortion and the sluggish diffusion in HEA are expected to contribute strong solid-solution hardening of HTSMA. In this study, multicomponent alloys composed of Ti-Pd-Pt-Ni-Zr were prepared and the phase transformation, shape memory properties, and mechanical properties were investigated.

Refractory metal, such as molybdenum and tungsten, are used in increasingly severe environments. Therefore, these materials are required to have superior mechanical properties, long life and excellent reliability. In this study, we developed newly Mo alloy dispersed Mo-base intermetallic compound for material forming such as hot extrusion die. This newly Mo alloy “MSB” exhibited superior mechanical properties compared with convention Mo alloy at temperatures below 1000℃. In addition, by adding a titanium alloy to the MSB, we have developed another alloy “T-MSB” that has high mechanical properties at higher temperatures. In the hot extrusion of brass, die made of these Mo alloys had 2.5 times longer tool life than the conventional Mo alloy die.

In the context of research of lighter and/or stronger high temperature materials in order to improve aeroengines, the present work shows an example of a powder metallurgy (PM) manufacturing route for TiAl alloys that could be used for low pressure turbine (LPT) blades processing. In this frame, two different alloys, Ti-47Al-1Fe-1Zr-1Mo-0.2Si (at. %) FZM and Ti- 43.5A1-4Nb-1Mo-0.1B (at.%) TNM-B1, were gas-atomized into powders, extruded, heat-treated and mechanically tested.

Electron beam melting (EBM) is one of the candidate manufacturing processes for TiAl alloys which have been considered as next generation high-temperature structural materials. The microstructure and mechanical properties of Ti-48Al-2Cr-2Nb (48-2-2) alloy bars fabricated using EBM were investigated, with a particular focus on the effect of processing parameters such as input energy density and building direction. We observed that the microstructure of the alloy bars fabricated using EBM depends strongly on the processing parameters used during the fabrication process of alloy. In particular, the alloy bars fabricated under appropriate processing parameters have a unique layered microstructure composed of duplex regions and equiaxed γ-grain regions (γ bands). Because of their fine microstructure and deformable soft γ bands, the alloy bars with the unique layered microstructure exhibit higher strength and higher ductility at room temperature (RT) than that of cast alloys. In addition, the alloy bars fabricated at an angle between the building direction and the loading axis of 45° show good fatigue properties at RT even without hot isostatic pressing treatment.

Titanium alloys are expected to be used as heat-resisting structural materials in the airplane and automotive industries. In this study, the creep properties of near-α Ti alloys consisting of a lamellar microstructure were studied. Ti–8.5wt%Al–8.0wt%Zr–2wt%Mo–1wt%Nb–0.15wt%Si alloy (alloy code, TKT34) and an alloy with 0.1 wt% of added boron (alloy code, TKT35) were used in this study. An ingot was hot forged at a temperature of 1,403 K and hot rolled (caliberrolling) at a temperature of 1,273 K to a reduction rate of approximately 90%. It then underwent solution treatment in a β single-phase region followed by air cooling. Finally, it was subjected to aging treatment for 28.3 ks at a temperature of 863 K and then air-cooled. Two solution treatment conditions were applied: a time of 1.8 ks at a temperature of 1,323 K (high temperature/short time (HS)) and a time of 3.6 ks at a temperature of 1,223 K (low temperature/long time (LL)). The average grain size of the prior β grains showed a tendency of the solution treatment temperature being low and the boron-added alloys tending to be small. The length and thickness of the lamellar of these alloys shortened or thinned owing to the addition of boron and at a low solution treatment temperature. The creep tests were carried out at an applied stress of 137 MPa and a temperature of 923 K in air. The creep rupture life of these alloys was excellent, in order of TKT35 (LL) < TKT34 (LL) < TKT35 (HS) ≦ TKT34 (HS). Therefore, the creep rupture life of these alloys was shown to be superior under the HS solution treatment condition as compared to the LL solution treatment condition. However, the minimum or steady-state strain rate of these alloys became slower in order of TKT 35 (LL)> TKT34 (LL)> TKT34 (HS) ≧ TKT35 (HS). The creep properties depended on the microstructure of the alloys.

The competitive effect of Nb and V additions on the high-temperature oxidation behavior of Ti- 30Al alloys were studied at 800°C in air. Oxidation performance increased with increasing Nb content, however, V additions eliminated the beneficial effect of Nb on oxidation performance, causing higher oxidation mass gains. In-situ high-temperature XRD by means of synchrotron source suggested dissolution of Nb 5+ but lower valence of vanadium ions in the TiO 2 oxide scale during oxidation. Dissolution of Nb and V ions with different valence in TiO 2 during oxidation could cause the beneficial and detrimental effects observed on the performance of high-temperature oxidation of Ti-30Al.

Tensile deformation behavior of γ-TiAl based alloys consisting of α 2 -Ti 3 Al/γ lamellar colonies, β-Ti grains, and γ grains were investigated by in-situ scanning electron microscopy and digital image correlation technique, in order to identify the role of each microstructure constituents in deformation. The alloy with nearly lamellar microstructure, in which the volume fraction of β/γ duplex ( V DP ) is 10%, shows elongation of only 0.14%, whereas the alloy with nearly globular β/γ duplex microstructure with V DP of 94% shows elongation of 0.49%. In α 2 /γ lamellar microstructure, obvious strain localization occurs along lamellae and develops at specific regions with loading. In the case of β/γ duplex microstructure, strain localization is observed in γ grains and in β phase regions near the β/γ phase boundary, although no obvious deformation is observed in the β grains. β/γ phase boundaries enhances room temperature ductility of TiAl alloys by inducing multiple slip in γ phase and deformation of β phase.

Titanium is extensively utilized in the aerospace industry due to its low density and excellent mechanical and chemical properties. Given that components in this sector are exposed to temperatures up to 873 K, representing 45% of the metal's melting point, understanding the mechanical properties in this temperature range is crucial for ensuring flight safety. This study focuses on examining the creep behavior of pure titanium to gain insights into its fundamental mechanical response. Creep was observed to occur at stresses exceeding micro-yielding levels around 297 K, primarily attributed to overcoming the pinning effect caused by interstitial atoms. Interestingly, at intermediate temperatures, an inverted primary creep phenomenon was noted, with an activation energy of approximately 240 kJ/mol within this range. This value, significantly larger than those associated with lattice or dislocation-core diffusions, suggests the potential movement of dislocations with interstitial atoms, similar to the diffusion of oxygen or nitrogen within titanium. Moreover, fracture strain exceeded 80% at temperatures surpassing 673 K, possibly resulting from grain boundary diffusion mechanisms akin to superplasticity. The activation energy for this mechanism, at 97 kJ/mol, is adequate for activating grain boundary deformation at intermediate temperatures.

The creep behavior of a γ-TiAl based alloy at 1073 K was investigated, examining three different microstructures: equiaxed γ (Eγ), γ/γ fully lamellar (FLγ), and equiaxed γ with α 2 phase on grain boundaries (Eγα 2 ). The aim was to understand the influence of lamellar interfaces and grain boundary α 2 phase on creep behavior. Initially, creep rates were consistent across all specimens upon loading. However, Eγ exhibited a gradual decrease in creep rate compared to Eγα 2 and FLγ. Notably, the minimum creep rate of Eγ was one order of magnitude lower than that of Eγα 2 and FLγ. Conversely, Eγα 2 and FLγ displayed a slight acceleration and the longest rupture strain, albeit with the shortest rupture time compared to Eγ. Upon microstructural analysis of of the creep-test specimens, it was observed that numerous dynamic recrystallized grains (DXGs) and sub-grains formed along grain boundaries and interiors in Eγ, whereas they were limited to the region along grain boundaries in FLγ. In contrast, very few DXGs were formed in Eγα 2 . These findings indicate that γ/γ interfaces inhibit the extension of DXGs into grain interiors, suggesting that the grain boundary α 2 phase effectively suppresses the formation of DXGs.

Interstitial carbon (C) in β-Ti, α-Ti, α 2 -Ti 3 Al and γ-TiAl phases present in the γ-TiAl alloys with and without substitutional elements (M: transition element) is quantitatively analyzed using soft X-ray emission spectroscopy (SXES), in order to reveal the effect of solute carbon on the phase equilibria. SXES for carbon analysis was used and the peak intensity of the second reflection of carbon Kα is analyzed using the fully homogenized sample having different C content under the optimum condition to make the accurate calibration curves. The obtained calibration curve is in an accuracy of ± 0.07 at. % C. In all heat treated alloys, no carbide is observed. In Ti-Al binary system, the α+γ phase region shifts toward higher Ti side, and the volume fraction of γ phase increases slightly with the carbon addition. In all system, carbon preferentially partitions into the α phase, followed by less partitioning in the γ and β phases in order. The carbon content in the β phase remains unchanged of almost 0.05 at. % regardless of carbon addition in Ti-Al-V system and the partition coefficient of carbon between the α and γ phases becomes larger in Ti-Al-V system than that in TiAl binary system.

In this study the effect of Widmanstätten-type morphology α 2 plates on creep has been investigated by preparing nearly equiaxed γ (N γ ) and nearly equiaxed γ having Widmanstätten-type α 2 plates within grain (Wα 2 ). Creep tests were conducted at 1073 K under constant stresses, high stress and low stress, in air. At the high stress, Wα 2 shows creep rate smaller than N γ in transient stage, both specimens show similar minimum creep rate and the creep strain at minimum creep rate is 3 % for Wα 2 and 10 % for N γ, since N γ shows prolonged primary region. In acceleration stage, both show similar behavior with rupture time of about 50 h and rupture elongation of 60 %. At the low stress, on the other hand, reverse behavior occurs, that is, W α 2 shows creep rate higher than Nγ in transient stage. The regions near grain boundaries progressively deformed for both specimens at high stress level, whereas deformed region is extended within grain interiors. From these results it is suggested that α 2 plate act as the obstacle for dislocation motion in the γ matrix at high stress and that interfacial dislocation promote the creep deformation at low stress.

Effects of microstructure constituents of α 2 -Ti 3 Al/γ-TiAl lamellae, β-Ti grains and γ grains, with various volume fractions on room-temperature ductility of γ-TiAl based alloys have been studied. The ductility of the alloys containing β phase of about 20% in volume increases to more than 1% as the volume fraction of γ phase increases to 80%. However, γ single phase alloys show very limited ductility of less than 0.2%. Microstructure analysis have revealed that intragranular fracture along γ/γ grain boundary occurred in γ single phase alloy whereas it does not along β/γ interphase in alloys containing β phase. In addition, local strain accumulations along β/γ interphase have been confirmed. The present results, thus, confirmed the significant contribution of β phase, especially the existence of β/γ interphase to enhancement of the room-temperature ductility in multicomponent TiAl alloys.

Either at higher temperatures or when a certain alloying element content is exceeded, γ-TiAl alloys contain the β phase (bcc) or its ordered derivate β o (B2). The relatively soft β phase can facilitate hot deformation, but β o is detrimental for creep strength and ductility. Thus, knowledge about β o →β phase transformation is desirable. Surprisingly, for the binary Ti-Al system it is under discussion whether the ordered β o phase exists. Also, the effect of alloying elements on the β phase ordering is still unclear. In the present work the ordering of the β phase in binary Ti-(39,42,45)Al and ternary Ti-42Al-2X alloys (X=Fe, Cr, Nb, Ta, Mo) which was experimentally investigated by neutron and high energy X-ray diffraction is compared with the results of first principles calculations using density functional theory. Except for Cr the experimentally determined and the predicted behavior correspond.

Erosion from solid and liquid particles in gas turbine and steam turbine compressors degrades efficiency, increasing downtime and operating costs. Conventional erosion-resistant coatings have temperature and durability limitations. Under an Electric Power Research Institute (EPRI) project, ultra-hard nano-coatings (~40 microns thick) were developed using Plasma Enhanced Magnetron Sputtering (PEMS). In Phase I, various coatings—including TiSiCN nanocomposites, stellite variants, TiN monolayers, and multi-layered Ti-TiN and Ti-TiSiCN—were deposited on turbine alloys (Ti-6Al-4V, 17-4 PH, Custom-450, and Type 403 stainless steel) for screening. Unlike conventional deposition methods (APS, LPPS, CVD, PVD), PEMS employs high-current-density plasma and heavy ion bombardment for superior adhesion and microstructure density. A novel approach using trimethylsilane gas successfully produced TiSiCN nanocomposites. Stellite coatings showed no erosion improvement and were discontinued, but other hard coatings demonstrated exceptional erosion resistance—up to 25 times better than uncoated substrates and 20 times better than traditional nitride coatings. This paper details the deposition process, coating properties, adhesion tests, and characterization via SEM-EDS, XRD, nanoindentation, and sand erosion tests.

The increasing steam parameters in modern high-efficiency fossil fuel power plants demand advanced materials with enhanced creep strength for operation under extreme temperature and pressure conditions. Tenaris has focused on developing ferritic-martensitic and austenitic grades for tube and pipe applications. At TenarisDalmine, efforts on ferritic-martensitic steels include ASTM Grade 23, a low-alloyed alternative to Grade 22 with 1.5% W, offering good weldability, creep resistance up to 580°C, and cost competitiveness. Additionally, ASTM Grade 92, an improved version of Grade 91, provides high creep strength and long-term stability for components like superheaters and headers operating up to 620°C. At TenarisNKKT R&D, austenitic steel development includes TEMPALOY AA-1, an improved 18Cr-8NiNbTi alloy with 3% Cu for enhanced creep and corrosion resistance, and TEMPALOY A-3, a 20Cr-15Ni-Nb-N alloy with superior creep and corrosion properties due to its higher chromium content. This paper details the Tenaris product lineup, manufacturing processes, and key material properties, including the impact of shot blasting on the steam oxidation resistance of austenitic grades. It also covers ongoing R&D efforts in alloy design, creep testing, data assessment, microstructural analysis, and damage modeling, conducted in collaboration with Centro Sviluppo Materiali.